Vehicle Linear and Rotational Acceleration, Velocity and Displacement During Staged Rollover Collisions
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2007-01-0732 Vehicle Linear and Rotational Acceleration, Velocity and Displacement during Staged Rollover Collisions Orion P. Keifer, Wesley C. Richardson, Peter D. Layson, Bradley C. Reckamp, and Thomas C. Heilmann Applications Engineering Group, Inc. Copyright © 2007 SAE International ABSTRACT vehicles and nearly any test surface. The test vehicles were instrumented to determine both the Four full scale vehicle rollover tests, about the roll angular and linear acceleration, from which the axis (X-axis), were staged using a sled attached to angular and linear velocities and displacements a large truck. Each vehicle was fitted with a nine- could be determined. accelerometer array that approximated the center of gravity and two single axis accelerometers METHODOLOGY attached to the roof adjacent to the A-pillar/roof junction. The acceleration data was retrieved for Vehicles three tests; however, the data recorder malfunctioned on the remaining test. Data was The test vehicles for the testing included the collected at 1000 hertz and processed to determine following: the linear and rotational acceleration with respect to each of the three vehicle coordinate axes. Vehicle VIN Color Rollover video and scene data were also collected 1989 Buick 1G4CU54C0K1668358 Gold to correlate vehicle rollover motion with the Park Avenue Ultra accelerometer data. 1994 Oldsmobile 1G3HN52L9R4818549 Blue 88 Royale INTRODUCTION 1997 Pontiac 1G2NE52TXVC866133 White Grand Am Full scale rollover tests have been conducted over 1995 Mercury 3MASM10J9SR647656 Green many years. Much of the work has been Tracer performed using various test sleds. One of the Table 1. Vehicle data. most common is the Federal Motor Vehicle Safety Standard (FMVSS) 208 sled test, which is Vehicle Mass kg Length m Width m SSF* conducted in accordance with SAE J2114, for Buick 1462 5.00 1.83 1.44 example the Malibu tests (Orlowski, et al., 1985 Oldsmobile 1573 5.08 1.88 1.36 and Bahling, et al., 1990). The FMVSS 208 test sled ramp angle is 23º and the test is conducted Pontiac 1307 4.75 1.73 1.34 using an initial speed of 30 miles per hour. The Mercury 1095 4.34 1.70 1.37 sled is decelerated to a stop in less than 3 feet and Table 2. Vehicle data. * Static Stability Factor (half the track a deceleration rate of at least 20 g’s for a width divided by the center of gravity height). minimum of 0.04 seconds. Sled The test procedure used for this work has a sled angle of 34º and a deceleration rate of The sled was manufactured using a utility trailer approximately 0.6 g’s; however, the tests required frame set side-ways. Two fixed axles were minimal apparatus that can be used for most attached to the frame. Two ramps, one for the front and one for the rear axles, were welded in place at an angle of approximately 34º (Figure 1). center accelerometer and the two channels for The designed ramp angle was determined using a each of the three legs. first order approximation, neglecting suspension compliance, such that all test vehicles would: first, be stable while the sled was stopped or accelerating and second, roll off the sled when the pusher truck was heavily braking. Rollover occurs when the line of action of the force through the center of gravity of the vehicle is forward of the front lip of the sled. That occurs when the sum of three angles exceed 90°. The three angles are the sled ramp angle, the angle formed by the ground and a line passing through the vehicle center of gravity, with the apex at the center of the Figure 2. Diagram of the sled angles. outboard tire, which is calculated using the Static Three channels of a 2g triaxial accelerometer, Stability Factor (SSF) and the friction angle due installed on the floor near the center of gravity, to braking, shown on Figure 2. In this first order were monitored. Two single axial 50g approximation, the braking deceleration required accelerometers were placed near the right and left to cause the vehicle to roll was calcuated between A-pillar roof intersection. The position and 0.35 and 0.4 g’s, depending on the test vehicle. orientation, with respect to the vehicle coordinate The front bumper of the pusher truck was axis varied from vehicle to vehicle, but in general removed and brackets fabricated for this test were were oriented mostly vertically with a forward and mounted on the frame members. The sled was outboard component as dictated by the interior then pinned to the frame brackets with two contour at the A-pillar to roof contour inside the transverse pins, one for each side. vehicle. Additionally, one data collection channel monitored a microphone, used for video to data collection synchronization. Figure 3 shows a photograph of the test equipment installed in one of the test vehicles. Figure 1. Photograph of the sled arrangement. Instrumentation A computer system was assembled to collect data, the details of which are in Appendix A. All data was collected with 12 bit resolution. Figure 3. Photograph of the nine-accelerometer array frame inside a test vehicle. The monitored accelerometers included a nine- accelerometer array, as proposed by Padgaonkar, Video et al. (1975) and Mital and King (1979), including three mutually perpendicular channels on the Video cameras were used to capture the roll-over from the side and from the front. Cones were placed on the test surface and measured as reference points for photogrammetric processing. The positions of the cones and video cameras were surveyed. TEST PROCEDURE The truck and sled were lined up on the test track and the vehicle was placed on the test sled. A balloon was popped adjacent to the test vehicle to provide synchronization between the data collection system and the video cameras. The video cameras captured the frame during which Figure 4. Buick the balloons popped and the data recorder captured the sound on the channel which monitored the microphone. The truck was accelerated and the speed of the truck was monitored with a Stalker radar gun. The truck steering was adequate to maintain a straight line of travel. As the truck crossed a predetermined line marked by cones, the driver locked up the brakes, causing the test vehicle to roll off the sled. When the vehicle came to final rest, a second balloon was popped adjacent to the final rest position of the vehicle, to synchronize Figure 5. Oldsmobile the video with the data collection system. The data was downloaded from the data collection system via an Ethernet connection. The vehicle was photographed and marks on the pavement were documented. RESULTS The roll data and distance traveled is summarized in Table 3. Buick Oldsmobile Pontiac Mercury Lead direction Driver Passenger Driver Driver Initial Vel. (kph) 55.5 54.7 56.3 56.3 Figure 6. Pontiac Rolls* 2 2 4 1/4 1 1/2 Yaw (final rest) 10ºCW 70º CCW 35ºCW 20ºCW Distance to Rest (m) 26.1 23.5 39.6 28.1 Drag factor 0.50 0.54 0.34 0.48 Table 3. Roll and distance data for the tested vehicles. * Including the initial 34°. Figures 4 through 7 show the damage received by the four vehicles during the rollover. Figure 7. Mercury Additional post-rollover photographs of the Recommended Practice J211-1 (SAE J211-1) for vehicles are enclosed in Appendix B. As defined Channel Frequency Classes CFC-60 and CFC- by the authors, the roll of the vehicle began when 180. It should be noted that the filtering frequency the following side (upper ramp) tires first lifted was the highest justified by the response of the off the ramp. The position of the test vehicle at accelerometers used. While it is less than the tire lift-off was determined from video analysis CFC-180 recommended for integration for speed and photogrammetry. The final rest position of and position, it exceeds the recommendation of the geometric center of the vehicle was CFC-60 for vehicle structural accelerations. determined by survey and checked using video Rotational acceleration was calculated using the analysis and photogrammetry. The initial speed formulation of Mital and King (1979). The of the test vehicle was determined by the peak rotational vectors were then transformed into the speed from Stalker data. Of note, the peak speed standard SAE vehicle coordinate system (positive was used from the Stalker data graphs for the x direction, forward, positive y direction to right Buick, Pontiac and Mercury. The graph for the and positive z direction, down). The transformed Oldsmobile was not retained and therefore, the rotational acceleration data showed a bias both recorded peak speed was used. before the roll started and after final rest, when the values should have been zero. Linear correction to the data during the period of rollover motion was made to the rotational acceleration, which was then numerically integrated to determine the rotational velocity. A similar bias was seen in the angular velocity data, which was removed by a linear correction. The corrected angular velocity data was numerically integrated a second time for the rotational displacement. The calculated rotational displacement was compared to visual Figure 8. Stalker data. Left peak is for the Buick, middle observation at final rest to determine the error, peak for the Pontiac and the right peak is for the thus checking the initial accelerometer accuracy as Mercury. well as the required corrections and vector transformations. The distance traveled during the roll and the Calculated Roll Visual Roll average drag factor was calculated and presented Vehicle Percent Error in Table 3. Displacement Displacement Buick 665º 686º 3% Accelerometer Data Processing Oldsmobile 785º 686º 14% Pontiac 1490º 1496º 0% Video and numerical data from the data collection system were first synchronized, and then the data Table 4.